Centrifugal compressors are used in various industries to pressurize a fluid (e.g., gas and/or liquid). For example, centrifugal compressors may be used in gas turbines, engines (e.g., turbochargers), natural gas pipelines, oil refineries, chemical processing applications, and other industry-specific applications. A centrifugal compressor includes an impeller that rotates about an axis. Blades are distributed circumferentially around the rotating axis. The blades are shaped such that the incoming fluid exits the impeller in a radial direction into a diffuser of the centrifugal compressor. The impeller imparts energy to the fluid as the fluid flows therethrough. The centrifugal compressor is typically configured to increase the pressure of the incoming fluid by a factor of at least 1.2 and often greater, such as up to 13.0 or more. A centrifugal compressor may be characterized by its operating range, which may be based on the difference between the mass flow at the choke point (or an upper limit on the mass flow) and the mass flow at the stall point (or a lower limit on the mass flow).
For many applications, it is generally desirable to increase the operating range of the centrifugal compressor. For example, high flow coefficient and high pressure ratio compressors may have relatively narrow operating ranges and may experience blockages along the shroud of the compressor as the operating point moves towards lower mass flows. Various designs have been proposed for increasing the operating range. For example, a tandem inducer may be added to the impeller to reduce shock losses. Tandem inducers typically include discrete inducer blades that are positioned upstream from corresponding main blades of the impeller such that a gap exists between a trailing edge of the inducer blade and a leading edge of a respective main blade. Although tandem inducers have been studied in the past as a possible modification for improving the performance of a centrifugal compressor, commercially-viable designs that improve flow conditions when the impeller is operating at lower mass flows have heretofore not been provided.